1. Field of the Invention
The present invention relates to an installation for the non destructive ultrasonic immersion testing of parts.
2. Description of the Related Art
In a preferential application of the invention, the installation is designed for testing tubular parts of turbomachines, such as fan casings of jet engines, it being understood that the invention could also be used for other types of part.
This type of part is known to be axisymmetric and to have manufacturing singularities such as regions having transverse end flanges for connecting to adjacent parts, connecting regions having variable inner and outer radii between the flange regions and the cylindrical wall of the tubular part, in which the air stream flows and which forms the principal region thereof, often having changes in thickness, holes, perforations or similar in the flange regions, etc. The casing is, moreover, made of a woven composite material consisting of a monolithic structure with three dimensional weaving of carbon fibers, of carbon fiber preforms and of an injected epoxy resin acting as a binder for the whole.
One example of such a tubular part to be tested is shown in FIG. 1, illustrating an outer casing 1 of a fan for a jet engine which has a longitudinal axis of symmetry X and is made of a high absorption composite material, which is why it is an ultrasonic transmission testing installation that is preferably chosen for a structural inspection of the material.
In particular, the casing 1 is defined by a cylindrical wall 2 (principal region) having variable thicknesses and delimiting the duct for air entering the fan, and by two transverse end flanges 3, 4 (flange regions) which terminate the wall 2 and which extend radially outward with respect to thereto. The transverse end flanges project from the cylindrical wall 2 via respective intermediate connecting regions 5 and 6, each having a small inner radius on the flange side and a large outer radius opposed thereto. Holes 7 are moreover created in the flanges, through which fastening members (not shown) can pass, to permit connection to other parts.
In addition, in order to test these composite tubular parts having transverse flanges, the size of which is, moreover, significant (the diameter can reach two meters for a coaxial length of approximately one meter), an ultrasonic immersion testing installation is used, such an installation being particularly well suited to detecting therein, in terms of searched-for defects, delamination or loss of cohesion of the plies of the woven fabric at their interface, microcracking around perforations and machined features, inclusions, foreign bodies, dry areas without resin or areas with excess resin, etc.
A prior art testing installation 9, using the ultrasonic immersion technique, is shown in part and schematically in FIG. 2 and comprises transducers for emitting and receiving ultrasound. The transducer 10 which emits an ultrasound beam is mounted on a support 11 located at the end of a robotic arm 12 and, in this example, is oriented toward the outer periphery of the casing 1 which defines the tubular part. The transducer 13 which receives the beam, and is aligned coaxially with the emitter transducer 10, is mounted on a support 14 located at the end of another robotic arm 15 and is then oriented toward the inner periphery of the casing 1. Thus, between the aligned transducers 10, 13, is the casing 1, of which the constituting wall, made of composite material, is then tested by a relative movement of the two synchronized robotic transducers with respect to the part 1.
Water jet nozzles 16, 17 are of course provided on the arms, coaxially with the transducers, and make it possible to facilitate the appropriate transmission or propagation of the beam of ultrasound waves by a continuous water jet in order to “couple” the transducers to the part, the latter being arranged in a container or a place specially conceived to that effect for recovering the liquid.
Although this installation gives good analysis results with respect to the ultrasound technique employed, it nonetheless presents drawbacks linked, in particular, to the geometry—having singularities—of the part.
Indeed, while such an installation tests the cylindrical wall effectively, with the transducers acting perfectly perpendicular thereto as in FIG. 2, it does not by contrast allow optimum accessibility to the regions having external transverse flanges 3, 4 and to the connecting regions 5, 6 of the fan casing 1, in particular the small radius connecting region of each of the flanges, on the side of the outer periphery of the casing.
This is due to the fact that the support 11 for the nozzle and for the transducer in question (the emitter in this example) is too bulky, with the result that, after having followed, perpendicular thereto, the outer periphery of the cylindrical wall 2, it cannot turn sufficiently in order to follow the region of curvature of the connector and the transverse flange in question. As shown by the chain line representation in FIG. 2, the support 11 for the nozzle 16 touches the cylindrical wall 2 as soon as the transducer 10, driven by the arm 12, starts to pivot in order to follow, perpendicular thereto, the regions in question 3 and 5, such that the positioning of the two transducers is incorrect and, as a consequence, the profile is not correctly followed and the testing is imperfect. Thus, some of the aforementioned defects might not be identified.
This problem does not arise for the support 14 for the nozzle 17 and for the other transducer 13, which is in no way encumbered by the transverse flange.
It should also be noted that synchronizing the two robotic arms, in order to keep the transducers in coaxial arrangement when following the flange regions and curved connectors, makes automating the installation more complex.
Furthermore, the testing itself of the tubular casing part, with its singularities, is relatively long since, after testing one transverse end flange, it is then necessary to test the opposite flange with, once again, the aforementioned problems.
Moreover, the installation makes it necessary to provide a container of considerable size in order to receive the fan casing and to recover the water sprayed by the nozzles.